1. Field of the Invention
The present invention relates to an actuator for use, for example, in a vehicle, particularly to an actuator provided with a locking mechanism capable of locking a piston rod with respect to a cylinder.
2. Description of the Related Art
An actuator is disposed, for example, in a safety device disposed in a vehicle in order to enhance safety of crews at the time of collision. The actuator is also disposed in the safety device or the like disposed in the vehicle in order to relax an impact applied to a pedestrian in a case where the vehicle collides with the pedestrian.
For example, when a seat belt is not attached to the crew in a normal state at the time of the collision of the front surface of an automobile, the crew fastened by the seat belt has a downward slipping posture, and a lower back belt is detached from pelvises. A so-called submarine phenomenon sometime occurs. When the submarine phenomenon occurs, crew's buttocks or lower limbs move forwards/downwards, and there is a possibility of secondary collision of the lower limbs with an instrument panel before the crew. As a device for suppressing the submarine phenomenon, a seat device has heretofore been known for operating an actuator to mechanically lift up a seat tip portion, when a sensor disposed on the tip portion of the automobile detects the collision. This constitution is described, for example, in Jpn. Pat. Appln. KOKAI Publication No. 2000-1136.
Moreover, when the pedestrian collides with the front surface of the running automobile, pedestrian's lower half body hits a bumper as the tip portion of the automobile, and therefore the pedestrian is thrown up onto a hood of the automobile in many cases. In this case, the pedestrian sometimes bumps his head or the like against the hood. Therefore, as a device for relaxing the impact at the time when the pedestrian is thrown up onto the hood, a hood device is known for operating the actuator to push up the hood by a predetermined amount, when the sensor disposed on the tip portion of the automobile detects the collision. That is, when the hood is pushed upwards, a gap is made between the hood and each device in an engine room. Therefore, when the pedestrian is thrown upwards and collides with the hood, the hood is deformed to absorb a part of energy by the impact. This constitution is described, for example, in Jpn. Pat. Appln. KOKAI Publication No. 2002-29367.
Additionally, in the actuator disposed in the above-described safety device, an output of a gas generation device is set in consideration of a collision speed or crew's weight. However, when the collision speed is high, or when the crews are heavy, an input load increases with respect to an operation power of the gas generation device, and a piston rod does not take a full stroke in some case.
In the conventional actuator disposed in the above-described safety device, relative movement of the piston rod with respect to a cylinder is locked in a state in which the piston rod takes the full stroke from one end of the cylinder. Moreover, once the piston rod completely protrudes from one end of the cylinder, the piston rod is held in the locked state.
Therefore, in the technique described in Patent Document 1 or 2, the relative movement of the piston rod with respect to the cylinder is not locked in a case where the piston rod does not take the full stroke because of the above-described factors or the like. Therefore, the sheet tip portion cannot be held in the lifted-up state, or the hood cannot be hold in the pushed-up state.
For this reason, in a hood device, seat device, buckle pretensioner or the like, there has been a demand for an actuator in which relative movement of a piston rod with respect to a cylinder can be locked in the vicinity of a position where the piston rod is stopped even in a case where the piston rod does not take its full stroke at the time of collision of an automobile.